The term "processing device" is to be understood as a device to which individual objects are supplied in series from one side, in which one object after the other undergoes processing and from which processed objects are conveyed away on the opposite side. Such processing devices are usually equipped with device parts for processing the objects and with device parts for conveying the objects through the device and the device is controlled to alternatingly process and convey. Processing may consist of only one processing step or of a plurality of successive part-steps. An example for this kind of processing device is a strapping device for crosswise strapping of substantially parallelepipedic packages or bundles.
The most various devices for strapping substantially parallelepipedic packages or bundles are known. These are devices with the help of which a tape, a string-like item or a film material is laid around the package or bundle and is then tightened and closed. Normally, a package or bundle is conveyed into such a device from one side, is positioned in a defined strapping position by a correspondingly arranged stop, is strapped and after strapping, is conveyed out of the device in the same direction, whereby a successive package is simultaneously supplied and positioned.
Devices of the kind named above are equipped in various manner. In the simplest of these devices, such as e.g. described in the publications U.S. Pat. No. 3,589,275 or U.S. Pat. No. 3,667,378, the packages or bundles are strapped transversely, i.e. substantially perpendicular to the supplying and conveying away direction either just once or possibly several times to produce a plurality of parallel transverse strappings. For crosswise strapping, i.e. for producing at least two strappings at right angles to each other, two of the mentioned devices are operated in succession. The packages receive a first strapping in the first device, and for the second strapping are then conveyed into the second device whereby the conveying path comprises a turn of 90.degree. or the objects are rotated by 90.degree., e.g. with a rotating device according to U.S. Pat. No. 3,901,138. With an arrangement of two such relatively simple devices a high output is achieved. If, however, one of the two devices fails, strapping must be stopped completely or the packages must, after the first strapping be resupplied to the still operable device by hand. With the help of an operator it is then possible to achieve at the most half of the usual output.
Cross-strapping devices are also known, i.e. devices in which a package or a bundle is strapped at least twice in a crosswise manner in two successive strapping steps or in substantially simultaneous strapping steps, whereby at least one strapping perpendicular to the conveying direction and at least one strapping parallel to the conveying directions is produced. In such devices, the packages or bundles are e.g. strapped perpendicular to the conveying direction, are then rotated by 90.degree. and are again strapped perpendicular to the first strapping. Such devices are e.g. described in the publication DE-3248788. The packages can also be supplied to a strapping device with one diagonal positioned parallel to the conveying direction and be cross-strapped in two strapping steps (direction of strapping oblique in relation to the conveying direction) which strapping steps at least partly overlap each other temporally whereby the object does not need to be moved between the strapping steps (e.g. described in publication DE-3303956). In a similar manner devices are operated in which the packages are strapped perpendicular to the conveying direction and in parallel to it without intermediate movement (quasi simultaneous transverse and parallel strapping), whereby the two strapping steps again advantageously overlap temporally at least partly. Such devices are e.g. described in the publication U.S. Pat. No. 5,078,057 or in the Swiss patent application No. 01631/97.
The so called cross-strapping devices as named above have the advantage of requiring considerably less space than an arrangement of two devices for transverse strapping only and comprising a rotation device between the two strapping devices. The performance of such cross-strapping devices (in cross-strapped packages per time unit) is, however, in most cases less than the performance of an arrangement of two devices for transverse strapping because in the latter arrangement the strapping steps can be absolutely simultaneous, which is not possible in the named cross-strapping devices. Furthermore, if a cross-strapping device is inoperative it is not possible even using personnel to maintain at least part of the output. In such a case, the packages or bundles must be stored intermediately or processing upstream of the strapping device must be interrupted.
In order to achieve higher output for cross-strapping carried out by strapping devices or, in general, to achieve higher output of processing devices according to the above definition and/or for reducing loss of processing through failure of such devices, it is known to arrange and operate two or possibly more than two such devices in parallel and to allot the objects to be processed to each of the devices by means of a switchpoint upstream of the devices. Using such an arrangement, the performance (in cross-strapped packages or generally speaking in processed objects per time unit) is increased, compared to one single such device, by a factor corresponding to the number of installed devices. If one of the devices fails the operation of the other devices is not impaired and at least part of the performance can be maintained. In such a case merely the switchpoint control needs to be altered. The disadvantage of this kind of arrangement is not only the fact that the switchpoint must be purchased, installed and maintained as an additional device but also the fact that the switchpoint and the parallel conveying means to and from the devices require a considerable amount of space, space which is usually not easily available, in particular when installations are extended. In the case of strapping devices, distribution to the parallel strapping devices prolongs the conveying path for packages or stacks which are not yet strapped. This is an important disadvantage in particular for not very stable stacks.
The object of the invention is to create an arrangement of per se known processing devices, in particular of cross-strapping devices, and to show a method for operating the arrangement, whereby compared to one only similar device, the inventive arrangement and the operating method are to give an increased performance as well as an increased security against loss of performance due to failure, but whereby, again compared to one single device the arrangement needs only a minimum of additional space and a minimum of additionally necessary conveying path.